For a while now I've been looking for the first female protagonist to shake the world of anime, and I think Saki may be it.

Some people reading this will say, what about Lady Oscar of Rose of Versailles? Sapphire of Princess Knight? Sazae-San? And Fujiko Mine?
Oscar and Sapphire both had to pretend to be men, Sazae-San while the main character is not internationally recognised unless someone wants to point out the World Record for longest animated series whenever someone thinks its the Simpsons and the fact that she's a housewife not an action heroine.
Fujiko Mine was originally designed to be multiple women and she's not the lead in Lupin the 3rd, only a foil.
The first real female protagonist in anime and Manga, not forced into a traditional role, not forced to hide the fact that they are female and not as a major secondary character is Saki Asamiya, debuted in 1975, a delinquent school girl turned undercover cop.
While the anime didn't come out until 1991, the Sukeban franchise existed in manga and live action for much longer, it served as a big game changer that paved way for the likes of Dirty Pair, Bubblegum Crisis and Project A-Ko, the rest is history as each generation has a new female protagonist to love.
Characters like Makoto Kino, Utena, A-Ko, Ryuko Matoi, pretty much any bad ass female character to ever wear the Sailor Fuku, they all owe a thanks to Saki Asamiya, the character who changed the anime landscape forever.